Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $247.26   11.323%   $275.2572   $275.26   $275.25   $275.30  
  Purchase #2 $155.74   13.192%   $176.2852   $176.29   $176.30   $176.30  
  Purchase #3 $240.68   7.184%   $257.9705   $257.97   $257.95   $258.00  
  Purchase #4 $240.73   11.782%   $269.0928   $269.09   $269.10   $269.10  
  Purchase #5 $50.31   4.531%   $52.5895   $52.59   $52.60   $52.60  
  Purchase #6 $215.77   9.545%   $236.3652   $236.37   $236.35   $236.40  
  Purchase #7 $71.43   7.123%   $76.518   $76.52   $76.50   $76.50  
  7 purchase totals = $1,221.92       $1,344.0784   $1,344.09   $1,344.05   $1,344.20